Thermoplastic blends of polypropylene resin and butyl rubber are known. U.S. Pat. No. 3,037,954 (Gessler et al) teaches a composition which comprises from about 5 to 50 weight per cent chlorinated butyl rubber and from 95 to 50 weight per cent polypropylene. The composition is prepared by a dynamic vulcanization process, in which the composition is simultaneously mixed and cured, thereby crosslinking the rubber and then dispersing it as small particles throughout the composition.
Additionally, U.S. Pat. No. 4,130,534 (Coran et al) describes elastoplastic blends of from 20 to 5 parts polypropylene and from 80 to 55 parts by weight butyl rubber. Coran et al specifically teach that these blends cannot be prepared with an organic peroxide as the sole vulcanizing agent.
Blends of butyl rubber and polyethylene are similarly well known.
U.S. Pat. No. 3,073,797 (Fischer et al) discloses a process whereby a blend of butyl rubber and polyethylene is cured with a combination of a peroxide and N-methyl-N-nitroso-4-nitrosoaniline. Comparative examples contained in this patent illustrate that inferior products result when peroxide is used as the sole curing agent.
U.S. Pat. No. 3,184,522 (Zagar) teaches compositions which comprise butyl rubber, polyethylene and a selected vulcanization accelerator.
U.S. Pat. No. 3,584,080 (Walker et al) teaches the vulcanization of a butyl rubber terpolymer with a free radical curing agent. A minor amount of polyethylene may be included in these compositions.
U.S. Pat. No. 3,265,770 (Edwards) teaches a complex process wherein a butyl rubber-polyethylene blend is first treated at high temperature with a peroxide in order to partially crosslink the polyethylene, and then treated at a lower temperature with a curative for the butyl rubber.
More recently, U.S. Pat. No. 3,909,463 (Hartman) discloses a process for grafting a polyolefin plastic with a rubber which may be butyl rubber, using a bi-functional phenol-aldehyde curing agent. Hartman surprisingly discloses that the resulting blends are merely grafted, and are not crosslinked.
Heretobefore, there has not been disclosed an elastoplastic composition comprising a blend of butyl terpolymer rubber and polypropylene wherein the blend is treated with a peroxide curing agent.